Gaseous fuel powered engines are common in many applications. For example, the engine of a locomotive can be powered by natural gas (or another gaseous fuel) alone or by a mixture of natural gas and diesel fuel. Natural gas may be more abundant and, therefore, less expensive than diesel fuel. In addition, natural gas may burn cleaner in some applications.
Natural gas has traditionally been introduced into an engine's cylinders via a solenoid operated admission valve. Although effective in some applications, a solenoid operated admission valve may not have the speed and/or force required to open fast enough or against high boost pressures in other applications.
One attempt to improve gas injection is disclosed in W.O. Patent 2009/071392 of Patrick et al, that published on Jun. 11, 2009 (“the '392 patent”). Specifically, the '392 patent discloses a fuel injector having a piezo actuator connected to a first piston, and a second piston connected to a valve needle. The first and second pistons are separated by a hydraulic coupling (i.e., a space) that is filled with fuel, and both pistons are surrounded by fuel. The piezo actuator is selectively energized to move the first piston toward the second piston, thereby causing movement of the needle valve. When the needle valve is pushed downward against a valve seat, filet injection is blocked. When the needle valve is pulled upward away from the valve seat, fuel injection is initiated.
Although the fuel injector of the '392 patent may be responsive, it may still be less than optimal. In particular, it may still lack sufficient movement and/or force for some applications. In addition, the injector may lack broad applicability to different types of fuel system, for example to gaseous fuel systems where the fuel is compressible and cannot be used within a hydraulic coupling. Further, while closing of the needle valve to end injections may be responsive during expansion of the piezo actuator, opening of the needle valve may be somewhat slower and/or unpredictable during retraction of the piezo actuator, without any other means of opening the valve. Finally, because of the inward valve opening design of the '392 patent, it may be possible for the needle valve to be inadvertently opened by high pressures in an associated combustion chamber, thereby causing interruption and/or instability in the ensuing combustion event.
The engine system of the present disclosure solves one or more of the problems set forth above and/or other problems in the art.